U.S. patent number 4,406,703 [Application Number 06/213,040] was granted by the patent office on 1983-09-27 for composite materials made from plant fibers bonded with portland cement and method of producing same.
This patent grant is currently assigned to Permawood International Corporation. Invention is credited to Bernard M. Guthrie, Robert B. Torley.
United States Patent |
4,406,703 |
Guthrie , et al. |
September 27, 1983 |
**Please see images for:
( Certificate of Correction ) ** |
Composite materials made from plant fibers bonded with portland
cement and method of producing same
Abstract
The specification discloses a method of producing composite
building materials from a mixture of plant fibers bonded with
portland cement. Plant fibers, cement and soluble silicates in
certain proportions are mixed and heated under pressure for a short
period to get physically stable product that can be cured under
atmospheric conditions to full strength. The plant fibers may
initially be pretreated with an aqueous solution containing
dichromate or permanganate ion prior to adding the cement to negate
the adverse effects of set inhibiting water-soluble compounds in
the fiber. Other chemicals may be added to modify the reaction and
improve the product.
Inventors: |
Guthrie; Bernard M. (Corvallis,
OR), Torley; Robert B. (Corvallis, OR) |
Assignee: |
Permawood International
Corporation (Philomath, OR)
|
Family
ID: |
26816443 |
Appl.
No.: |
06/213,040 |
Filed: |
December 4, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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118503 |
Feb 4, 1980 |
|
|
|
|
Current U.S.
Class: |
106/731;
106/609 |
Current CPC
Class: |
C04B
18/28 (20130101); C04B 28/26 (20130101); C04B
28/04 (20130101); B28B 1/525 (20130101); C04B
28/04 (20130101); C04B 18/26 (20130101); C04B
22/08 (20130101); C04B 24/12 (20130101); C04B
40/00 (20130101); C04B 28/26 (20130101); C04B
7/02 (20130101); C04B 18/26 (20130101); C04B
22/08 (20130101); C04B 24/12 (20130101); C04B
40/00 (20130101); Y02W 30/97 (20150501); Y02W
30/91 (20150501) |
Current International
Class: |
C04B
18/28 (20060101); C04B 28/00 (20060101); C04B
28/04 (20060101); C04B 28/26 (20060101); B28B
1/52 (20060101); C04B 18/04 (20060101); C04B
007/353 () |
Field of
Search: |
;106/76,81,93,99
;8/115.5,116 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Poer; James
Attorney, Agent or Firm: Klarquist, Sparkman, Campbell,
Leigh, Whinston & Dellett
Parent Case Text
RELATED APPLICATION
This application is a continuation-in-part of our copending
application Ser. No. 118,503, filed Feb. 4, 1980 now abandoned.
Claims
We claim:
1. In a method of producing composite materials from plant fibers
containing water-soluble compounds and portland cement the step
comprising contacting the plant fibers with a material selected
from the class consisting of dichromate ion and permanganate ion to
substantially negate the adverse effects of the water-soluble
compounds in the plant fibers on the setting of the cement.
2. A method of producing composite materials from portland cement
and plant fibers containing cement set inhibiting compounds
comprising:
contacting plant fibers with dichromate ion;
mixing the treated plant fibers with portland cement and water;
molding the mixture into a predetermined configuration; and
curing the molded mixture.
3. The method of claim 2 wherein the plant fibers are wood
fibers.
4. The method of claim 3 wherein the plant fibers are contacted
with an aqueous solution containing dichromate ion in an amount
ranging from approximately 0.5% to 8% of the oven dry weight of the
plant fibers.
5. The method of claim 3 wherein the ratio of portland cement to
plant particles is approximately 0.5:1 to approximately 4:1
according to weight.
6. The method of claim 2 wherein the water to cement ratio is
approximately 0.5 to approximately 2 according to weight.
7. The method of claim 2 wherein the plant fibers are contacted in
an acidified aqueous solution containing dichromate ion for a
period of time sufficient to permit the dichromate ion to react
effectively with the cement set inhibiting compounds at or near the
surface of the plant fibers.
8. The method of claim 2 wherein the fibers are contacted with a
sulfite solution prior to treating them with dichromate ion.
9. The method of claim 2 wherein the plant fibers are contacted in
an aqueous solution containing the dichromate ion and also
containing aluminum sulfate in an amount ranging from approximately
0.5% to approximately 6% of the oven dry weight of the plant
fibers.
10. The method of claim 2 and further comprising the step of adding
calcium chloride to the mixture prior to molding in an amount
ranging from approximately 0.5% to approximately 5% of the weight
of the cement.
11. The method of claim 2 wherein triethanolamine is added to the
mixture prior to molding the same.
12. The method of claim 2 wherein the mixture is molded under
compression at approximately 150 psi to approximately 600 psi.
13. The method of claim 12 wherein the compression is carried out
at a temperature of between about 100.degree. F. and 220.degree.
F.
14. The method of claim 13 wherein the compression is carried out
in a substantially saturated atmosphere.
15. The method of claim 2 wherein the fibers are western red
cedar.
16. The method of claim 2 wherein the fibers are douglas fir.
17. The composite material produced by the method of claims 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 16.
18. A method of producing composite material comprising the steps
of:
contacting plant fibers containing cement set inhibiting compounds
with an aqueous solution containing dichromate ion in an amount
ranging from approximately 0.5% to approximately 8% of the oven dry
weight of the plant fibers and aluminum sulfate in an amount
ranging from approximately 0.5% to approximately 6% of the oven dry
weight of the plant fibers;
holding the aqueous plant fibers/dichromate/aluminum sulfate
mixture for a period of time sufficient to permit the dichromate
ion to react effectively with the cement set inhibiting compounds
in the plant fibers;
mixing an alkaline substance into the last mentioned mixture in an
amount sufficient to substantially neutralize the mixture;
mixing portland cement into the last mentioned mixture in an amount
sufficient so that the ratio of portland cement to plant fibers is
approximately 1:1 to approximately 4:1 according to weight;
molding the last mentioned mixture into a predetermined
configuration; and
curing the molded mixture.
19. The method of claim 18 wherein the alkaline substance is sodium
silicate.
20. The method of claim 18 wherein the ratio of water to cement in
the mixture is from approximately 0.3 to approximately 2 according
to weight.
21. The method of claim 18 and further comprising mixing calcium
chloride into the mixture prior to molding in an amount ranging
from approximately 0.5% to approximately 5% of the weight of the
cement.
22. The method of claim 18 wherein triethanolamine is added to the
mixture prior to molding in an amount of between 0.05 and 0.15% of
the portland cement.
23. The method of claim 18 wherein the mixture is molded under
compression at approximately 150 psi to approximately 600 psi.
24. The method of claim 18 wherein the plant fibers are western red
cedar.
25. The method of claim 18 wherein the plant fibers are douglas
fir.
26. A method of producing composite material comprising the
steps:
contacting plant fibers containing cement set inhibiting compounds
with an aqueous solution containing dichromate ion in an amount
ranging from approximately 0.5% to approximately 8% of the oven dry
weight of the plant fibers and aluminum sulfate in an amount
ranging from approximately 0.5% to approximately 6% of the oven dry
weight of the plant fibers;
allowing the aqueous plant fibers/dichromate/aluminum sulfate
mixture to stand for a period of time sufficient to permit the
dichromate ion to react effectively with the cement set inhibiting
compounds in the plant fibers;
mixing an alkaline substance into the last mentioned mixture in an
amount sufficient to substantially neutralize the mixture;
mixing portland cement into the last mentioned mixture in an amount
sufficient so that the ratio of portland cement to plant fibers is
approximately 1:0.5 to approximately 4:1 according to weight and so
that the water to cement ratio is approximately 0.5 to
approximately 1.2 according to weight, and also mixing calcium
chloride into the last mentioned mixture in an amount of
approximately 2% of the weight of the cement;
forming the last mentioned mixture into a mat;
cutting the mat into discrete portions;
placing the mat portions between pre-heated upper and lower caul
plates;
conveying the caul plates with the mat portions therebetween into a
stack press;
compressing the mat portions in the stack press at a psi of from
approximately 150 to approximately 600 in an atmosphere of live
steam for a period of time sufficient to cause the cement to set
sufficiently to prevent the plant fibers returning to their
uncompressed position;
removing the upper and lower caul plates and the compressed mat
portions from the stack press; and
removing the compressed mat portions from between the upper and
lower caul plates.
27. The composite material produced by the method of claims 18, 19,
20, 21, 22, 23, 24, 25 or 26.
28. In a method of producing composite materials from plant fibers
and portland cement the steps of mixing together plant fiber,
portland cement and a soluble silicate as 41.degree. Be aqueous
solution in amount greater than four but less than twenty-four
percent by weight, based on the weight of the cement, molding the
mixture into a predetermined configuration and while maintaining
said molded configuration, rapidly heating the molded mixture to a
temperature in excess of 140.degree. F. for a period of time
sufficient to effect setting of the mixture to a degree of set
whereby said fibers are restrained from movement within said
configuration.
29. The method of claim 28 wherein said molded configuration is
heated to a temperature of between 175.degree.-180.degree. F.
30. The method of claim 28 wherein said silicate is waterglass and
comprises between about eight to twenty-four percent by weight of
portland cement.
31. The method of claim 30 wherein said waterglass comprises
between about eight to sixteen percent by weight of the weight of
the portland cement.
32. The method of claim 30 wherein said waterglass is selected from
the class consisting of aqueous solutions of sodium silicate and
potassium silicate.
33. The method of claim 28 wherein said fibers are contacted with
acidifying agent prior to mixing with the cement and silicate.
34. The method of claim 28 wherein said fibers are contacted with
dichromate ion-containing solution prior to mixing with the cement
and silicate.
35. The method of claim 28 wherein said plant fibers comprise
wood.
36. The method of forming a composite of plant fiber and portland
cement which comprises the steps of:
contacting plant fibers with an acidifying solution,
mixing the fibers with a soluble silicate and portland cement, the
silicate being present as 41.degree. Be aqueous solution in amount
in excess of four but less than twenty-four percent by weight of
the weight of portland cement,
placing the resulting mixture under pressure and submitting the
same to an atmosphere of steam for a period sufficient to raise the
temperature of the mixture to between 140.degree. F. and
200.degree. F.,
thereafter removing the mixture from said atmosphere and releasing
the pressure,
thereby to form a substantially dimensionally stable composite of
said portland cement and fibers which can cure to full strength
without deformation of the composite.
37. The method of claim 2 wherein subsequent to the step of
contacting the plant fibers with dichromate ion the plant fibers
are subjected to the further step of mixing the fibers with a
soluble silicate present as 41.degree. Be aqueous solution in an
amount in excess of four but less than twenty-four percent by
weight of the weight of the portland cement.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to roofing and siding
construction materials. More particularly, the present invention
concerns a method of producing such construction materials from a
mixture of plant fibers and portland cement.
There is an ever-increasing demand for construction materials
having some or all of the following characteristics: relatively
light weight, fireproof, waterproof, nailable, odorless, insulative
and relatively inexpensive. In spite of the attractive properties
of a dense building material consisting of plant fibers such as
wood fibers bonded with portland cement, no such product has
effectively been marketed. Only porous products consisting of
excelsior bonded with portland cement or a magnesium oxychloride
cement have seen limited use. It is difficult to bond portland
cement to plant fibers because water-soluble compounds in the
fibers inhibit the setting of the cement. Among these compounds are
hemicelluloses, tannins, sugars and others. Heretofore, an
effective agent for negating the adverse effects of these
water-soluble compounds in the fibers has not been discovered.
Another problem is the effect of the motion of the fibers during
the setting of the portland cement. Any springback of the fibers
after being compressed or swelling and/or shrinking with absorption
or desorption of water during the setting of the portland cement
will fracture the tiny crystallities of cement as they slowly form.
Since the strength of the cement depends on the intermeshing of
these crystallites, their disruption will greatly weaken the cured
product.
Heretofore efforts to control the adverse effects of these
water-soluble inhibitors in a wood or other similar fiber composite
material utilizing portland cement as a binder, have resulted in
five different approaches:
(1) extracting the inhibitors;
(2) accelerating the rate of set of the portland cement;
(3) increasing the strength of the composite material by the
addition of resins;
(4) coating the surfaces of the fiber particles with materials
compatible with cement (mineralization); and
(5) changing the composition of the portland cement to obtain a
material less sensitive to the inhibiting action of the
water-soluble compounds.
To date, none of these approaches has been economically
successful.
SUMMARY OF THE INVENTION
Among the objects and advantages of the present invention are to
provide:
low cost composite building materials particularly adapted for
exterior use;
composite building materials made from plant fibers bonded with
portland cement having the following properties:
(1) a weight which is substantially less than that of comparable
composite building materials made from a sand/cement mixture;
(2) a resistance to fire;
(3) an ability to be nailed into place;
(4) an ability to be molded into attractive shapes or sheets, and
sawed with readily available tools;
(5) sufficient strength to withstand blows from hammers during
construction without cracking; and
(6) resistance to the deleterious effects of sunlight, rain,
freeze-thaw conditions and insects;
a process for manufacturing building materials of the
aforementioned type which does not produce ecologically harmful
effluents;
building materials made from a plant fiber/portland cement mixture
in which the adverse cement set inhibiting effects of the
water-soluble compounds in the fiber are effectively negated;
a process of manufacturing building materials from the
aforementioned mixture in which the time that portions of the
mixture must be held under compression is reduced to a minimum;
and
a method of producing composite building materials from a mixture
of plant fibers with portland cement in which a wide variety of
plant fibers may be utilized.
In accordance with the present invention, composite articles of
portland cement and fibrous material obtained from various plants
are formed by mixing the fibers with portland cement and a water
soluble silicate, the latter being present in amount by weight
greater than about four percent of the weight of the portland
cement and up to about twenty-four percent, and thereafter
maintaining the mixture under pressure while heating the same to a
temperature sufficient substantially to accelerate the setting of
the mixture. This causes the mixture to set sufficiently hard to
prevent springback or swelling of the fibers thus permitting the
application of pressure to be terminated in a short time and the
formed article or composite to be cured to final strength without
further application of pressure or heat. When fibers containing
large amounts of cement set inhibiting chemicals are being used the
fibers preferably are treated with an aqueous solution of a
dichromate or permangenate salt prior to mixing them with the
portland cement and water soluble silicate. Various process
modifications may be made as described in more detail hereinafter.
We have discovered that dichromate or permanganate treatment of the
fibrous material somehow inhibits the usual adverse effect on the
setting of portland cement which has been observed with some
fibrous plant material.
Other objects and advantages of the present invention will be
apparent from the following detailed description of a preferred
embodiment thereof and from the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general schematic illustration of the overall operation
of the manufacturing process; and
FIG. 2 is a graph showing the relationship between compressive
strength and curing time for concrete.
FIG. 3 is a graph illustrating the effect of the addition of sodium
silicate upon the strength of a portland cement-fiber mixture.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with a preferred embodiment of the invention, plant
fibers are mixed with a soluble silicate such as an alkali metal
silicate solution (water glass) and portland cement. This mixture
is placed in molds and compressed. It is then subjected to heat so
as to raise the temperature of the mixture to greater than
140.degree. F. such as by placing it in an atmosphere of live
steam. This causes the mixture to set up sufficiently within a
short period of time, i.e., within fifteen to sixty minutes, as to
resist any tendency of the fibers to swell or springback. Thus, the
pressure applied to the molded articles can be relieved and the
articles permitted further to cure at ambient temperatures to final
strength. The articles will have enough strength after fifteen or
twenty minutes in the mold to permit trimming and sawing to be
performed. Within about twenty four hours, the articles will have
about eighty percent of their ultimate strength and could be
shipped at that time. Longer periods in the molds will increase the
out-of-mold strength.
It has been found that the alkali metal silicate should be present
in concentration greater than about four percent dry weight in
proportion to the amount of portland cement. Such amount, by some
mechanism not understood, causes the mixture rapidly to set up when
heated, thus eliminating the need to maintain a molded article
under pressure a lengthy period.
When fibers containing amounts of set inhibiting compounds
sufficient to interfere with the set of the cement are utilized, it
has been found the deleterious effect of such compounds can be
negated or diminished in large part by pretreating the plant fibers
with an aqueous solution of an alkali metal or other water soluble
salt of dichromate or permanganate ion. The wetted fibers are
allowed to stand for a period of time sufficient to permit the
dichromate or permanganate ion to react with substantially all of
the cement set inhibiting compounds in or near the surface of the
fibers. Thereafter, the silicate material and portland cement are
added to the now treated wood fibers, with or without other useful
chemicals, and the mixture is molded under pressure as described
above. The residual products of the pretreatment do not harm the
strength of the cement, nor does the treatment when properly
controlled appear to degrade the strength of the fibers.
In the case of dichromate ion, the reaction with the fibers can be
accelerated by acidifying the dichromate solution. In such a case
it is necessary after fiber treatment to neutralize the remaining
solution at the conclusion of the dichromate treatment period with
a suitable alkaline solution or solid. It may be desirable in some
instances to add a cement set accelerator along with the portland
cement in order to reduce the molding time.
Prior to treating the fiber with the dichromate solution, the fiber
may first be treated with a sulfite solution. This treatment
enhances the strength of the composite product by a mechanism
discussed subsequently.
In the case of treatment with permanganate ion, the permanganate
solution is preferably on the alkaline side.
Plant Fibers
Different plant fibers have varying types and amounts of
water-soluble compounds therein which can inhibit the setting of
the portland cement. Some, such as hemlock, have little or none. On
the other hand, western red cedar has a high percentage of such
compounds, but because of the resistance of the fiber thereof to
decay and insect attack, it is a useful source of fiber for the
composites of the invention. Other woods such as douglas fir are
less difficult to bond with portland cement but dichromate
treatment does lessen the setting time of cement mixed with douglas
fir fibers. The present invention may also be extended to fibers of
hard woods such as oak and walnut and of other plant materials,
such as, for example, straw, bagasse, sisal, and the like, which
have relatively high tensile strength since it is contribution of
this property of the fibrous material which is sought.
The fiber mixed with the cement can be in any of a variety of forms
depending upon the nature of the fiber source, the geometry of the
finished articles and the characteristics or qualities desired in
such articles. The fiber can be in the form of strands or stringy
material when made from grasses, bagasse, cedar bark, and like
sources and a product of maximum tensile strength is desired. Wood
flakes or planer shavings as used in composite resin bonded
products heretofore can also be used. If a product with a smoother
surface is desired, wood can be used in the form of the product
produced by hammer milling wood flakes or planer shavings and
passing them through screens having openings of selected maximum
size which may be from 1/16 inch to 3/4 inch depending upon the
qualities desired in the finished product.
Soluble Silicate
We have found that the incorporation of a substantial quantity of a
soluble silicate in the fiber-cement mix enables the mix to be set
up rapidly, i.e. within one hour or less, by the application of
heat, to the point where the set mass is dimensionally stable and
has sufficient strength that it can be removed from a pressure mold
and allowed to cure further under ambient atmospheric conditions.
Thus the pressure mold used for the initial set is quickly
available for reuse.
The soluble silicate is preferably added as water glass or potash
waterglass. It can be mixed with the fibers before mixing with the
portland cement or it can be added after the cement and fibers have
been mixed if added as a freshly prepared gel. The silicate can
also be added in the dry form if sufficient water is also added to
dissolve the same.
We have found that with Douglas fir fiber, if the silicate is
present as 41.degree.Be' waterglass in amount greater than about
eight percent based on the dry weight of portland cement, the
fiber-portland cement mix can be set by the application of heat and
pressure within fifteen to twenty minutes to a relatively
dimensionally stable condition. Preferably the water glass is
present in amount between eight and sixteen percent of the cement.
Increase in the percentage of waterglass up to about twelve percent
will further increase the dimensional stability of the product.
However, still further increase in the amount of waterglass does
not improve the dimensional stability of the product. Moreover, the
ultimate strength of the product reaches a maximum when waterglass
is present between about twelve and sixteen percent. On the other
hand the out-of-the mold strength increases substantially
proportionately to the amount of waterglass present. See FIG.
3.
Treating Agent
Dichromate ion is the base agent which we have found to have the
capability significantly to negate the adverse effects of the
cement set inhibitors in plant fibers. However, we have found that
permanganate ion also shows a capability in this respect, although
to a lesser extent than dichromate ion. Because dichromate ion
treatment is much to be preferred, the following detailed
description will focus primarily on the use of such ion.
The dichromate ion or permanganate may be supplied in the form of
alkali metal or other soluble salt. Two readily available sources
of dichromate ion are potassium dichromate and sodium dichromate
dihydrate. Other water-soluble metal dichromates, e.g. calcium
dichromate, may also be utilized.
Dichromates are considered to be a potentially hazardous chemical.
Therefore, it is desirable that water-soluble dichromate
essentially be absent from the finished product. Enough dichromate
ion must be present during the pretreatment of the fibrous material
to ensure essentially complete reaction of the cement set
inhibitors on the surface of the material with dichromate.
The manner in which the dichromate ion reacts with the
water-soluble plant compounds to negate their cement set inhibiting
effects is not completely understood by us. In the finished product
it is possible that the chromium ends up as insoluble chromic oxide
(Cr.sub.2 O.sub.3) which may be chemically bound up with the
hardened cement or with the original soluble compounds in the plant
fibers, or both.
It has been determined that dichromate ion must be present in the
aqueous pretreating mixture in an amount ranging from approximately
0.5% to approximately 8% of the oven dry weight of the fibrous
material. The precise amount of dichromate necessary will depend
upon the fibrous material since they vary widely in the types and
amounts of water soluble compounds which inhibit the setting of
portland cement. The amount of dichromate ion added is that amount
which is just sufficient to react with the inhibitors present at or
near the surface of the fibrous material being treated, as
determined by experimentation.
In the fiber particles, particularly of wood, absorb water during
the initial stages of the set of the concrete, the subsequent
swelling or other shifting or curling of the particles will disturb
the growth of the cement crystallites and seriously weaken the
final strength of the composite product. Therefore, it is important
that this water absorption be completed by saturating the fibers
before the onset of the cure of the cement. This saturation is
preferably accomplished during the treatment of the fibers with the
dichromate by mixing the fibers with an aqueous solution of the
dichromate salt having more water present than is required to
saturate the fibers.
The water required for the hydration of the cement can be computed
as being about 25% of the cement present. Sources of water to meet
this requirement--as in the case of the saturation of the
fibers--can be water available from the solutions of the chemicals
and from free water if necessary. From many experiments with
various wood fibers, we have determined that the total water
necessary is the amount required to saturate the wood fiber plus
25% of the weight of the portland cement present. Wood will absorb
moisture to about 30% of its wet weight. Thus, the amount to
saturate wood fibers is equal to ##EQU1## For composites of
acceptable strengths, the weights of the composites after air
drying were plus or minus about 10-15% of the empirical values
calculated as described.
In practice, additional water in the amount of an excess of 20-40%
of the theoretical water were added to facilitate the chemical
treatments of the fibers and to improve the mixing and molding
characteristics of the composite.
The length of time necessary for the appropriate action of the
dichromate on the fibers depends on a number of factors such as the
concentration of the solution of the dichromate being used, the
reaction temperature, the structure of the fibers, the various
chemical substances naturally present in the fibers and their
amounts, the acidity of the aqueous phase and the possible presence
of a surface active (surfactant ) material. However, the actual
time of treatment can only be determined experimentally.
It will be recalled that it is an object of the invention that the
time required for the composite to be held under pressure in the
mold be as short as possible, to increase the production rate of
composite products and lower the manufacturing costs by efficient
use of press and molds. Only enough press time should be allowed
that the composite product, when released from the mold, will
retain its structural stability during the final set of the
portland cement.
It has been found that acceptable production rates can be realized
with mold retention times from 30 to 90 minutes, although using
waterglass in the quantities hereinbefore mentioned enables the
mold retention time to be reduced to as short as fifteen minutes.
In order to accomplish this production rate, the quantity of the
cement set inhibitors, if present in the fiber in substantial
amount, must be reduced so that they will not escape from the
fibers and act on the cement even at the elevated temperatures used
during the molding cycle.
The necessary period for the dichromate ion to react with the
cement-set inhibitors so as to attain such production rate will
vary as indicated above. With some fibers such as hemlock, little
or no reaction time is required. With douglas fir which is recently
cut, a few minutes at room temperature may suffice. With more
difficult fibers such as western red cedar, 10 or 15 minutes at the
temperature of boiling water may be required. It is desirable that
in carrying out these reactions the concentration of dichromate be
limited to provide the amount needed, the acidity level be adjusted
to provide sufficient speed of the reaction, and the lowest
effective temperature used. The levels of these operating
parameters must be determined experimentally with the fiber species
to be used. Departure from the peferred conditions may cause loss
of strength in the cured composite product because of degradation
of the fibers as well as poor cure of the cement.
Depending on the fiber, sodium dichromate dihydrate in the amount
of 0.5-8% of the fiber (dry weight) being treated is adequate to
react with the cement set inhibitors.
During the dichromate treatment, surfactants should be avoided.
They ct to accelerate the release of the cement set inhibitors,
thus disturbing the desired chemical condition at the interface
between the fibers and the portland cement. In fact, if a
surfactant is present at this point, the final product strength can
be seriously impaired.
It should be understood that separate treatment of the wood with
dichromate prior to the addition of the portland cement is not
absolutely necessary. The dichromate could be added to an already
prepared moist wood fibers/portland cement mixture. However, the
strength of the final product is better if the fibers are
pretreated with dichromate before the addition of the cement. The
last mentioned technique ensures that the set inhibitors are
substantially negated before the cement contacts the fiber.
The Acidifying Agent
A wide variety of acidifiers may be utilized. It has been found
that aluminum sulfate provides a good level of acidity, somewhat
buffered by the hydrolytic capacity of the aluminum ion. On the
other hand, unbuffered sulfuric acid is harmful. Aluminum chloride
may also be used but it is desirable not to have the corrosive
chloride ion present. Other acidic salts may also be useful but
have not yet been tried.
Usually, aluminum sulfate to the extent of 0.5 to 6% of the fiber
weight is adequate.
The Reducing Agent
The use of sulfurous acid has been shown to be beneficial in our
process for bonding wood fibers to portland cement, although the
mechanism is not understood. If the wood such as fir is first
treated with a dilute, weakly acid solution of sodium sulfite
followed by the addition of dichromate and then waterglass and
cement, a substantially increased strength of the composite is
obtained. Moreover, any excess of dichromate over that normally
required for the reaction with the fibers is reduced and thus
removed. The weakly acid system can be achieved by mixing a
solution of sodium sulfite with a solution of alum, using a
solution of sodium bisulfite, or using a solution of sodium
thiosulfate (hyposulfite). Strongly acidic solutions must be
avoided to prevent damage to the cellulose fibers.
The Alkaline Agent
After the completion of the dichromate treatment, the solution
remaining on the fibers is a weakly acidic solution of chromium
sulfate and aluminum sulfate, or chromium chloride and aluminum
chloride, etc., depending on the acidic system used. In order to
provide a neutral condition more favorable to the setting of the
portland cement, this acidity of the fibers should be neutralized
by the controlled addition of an alkaline substance to bring the pH
to 7.0 or above. Aqueous solutions of sodium hydroxide, potassium
hydroxide, sodium carbonate and the like may be used. Solids such
as lime (calcium oxide) may also be used but their performances
will be less satisfactory because of the necessity of their first
dissolving in the moisture present. For example, slaked lime is
only sparingly soluble and thus the neutralization reaction
progresses slowly.
The substance preferred is sodium silicate. Even in small amounts
it has the advantage of precipitating calcium, aluminum and
chromium silicates which might act as cements, mineralize the fiber
surfaces, and impart a degree of waterproofness to the composite
product. The mineralization technique is discussed in U.S. Pat. No.
2,623,828 issued to Dove. If waterglass solution is utilized
instead of a solid alkaline substance, the water in the solution
must be taken into account when establishing the appropriate
portions to yield the desired water/cement ratio.
The solution of sodium silicate preferably used is a 2:1 dilution
of 41.degree. Be sodium silicate in water. For neutralization of a
20% aluminum sulfate acidifying solution, a ratio of at least twice
the volume of sodium silicate solution for each volume of aluminum
sulfate solution is preferred. Again, the proper water balance must
be observed and higher or lower concentrations of the sodium
silicate may be used as the case may require. In particular, higher
concentrations may be utilized to obtain a rapid set at elevated
temperatures as hereinbefore described.
The Portland Cement
Type III portland cement is preferred because of its high early
strength characteristic. Type I-II portland cement may also be
used, however. The cement is mixed with the moist fibers after the
completion of the dichromate reaction, if such is carried out, and
preferably after addition of the alkalizing agent and adjustment of
the pH level thereof to a more or less neutral state. Other more
rapidly setting cements such as REGULATED SET (trademark) may also
be utilized in order to minimize the deleterious effects of the
cement set inhibitors in the fibers. However, they are much more
expensive than portland cement and may have other detracting
properties.
The ratio of portland cement to fibers has a strong relationship to
the ultimate strength characteristics of the finished product. The
cement/fiber ratios may be vaired considerably, producing products
having somewhat differing characteristics. In general, the more
dense the finished composite material (achieved by greater
compression), the better is its weather proofness and strength when
the fiber to cement ratio is constant. On the other hand, for
strength only, there is an optimum ratio of fiber to cement
depending upon the type of fiber used. In the case of wood fiber
ratios ranging from approximately 0.5:1 to approximately 4:1, of
portland cement to oven dry wood fiber, according to weight, will
produce composite materials of acceptable strength and weathering
properties. Strength appears to peak at cement/wood fibers ratio of
approximately 1.3:1 to approximately 1.7:1. Size and shape of the
particles are also important. Generally, acicular particles or flat
blades are superior to short, stubby particles.
At the higher end of the preferred range mentioned above, e.g.
portland cement to fiber ratios of approximately 2.75 or so, higher
densities above 75 pounds per cubic foot will be obtained,
especially at pressures in the press over 150 psi. At ratios of 1.3
to 1.5:1 and pressures of 500 psi, products having densities of
65-75 pounds per cubic foot are readily prepared.
The Cement Set Accelerating Agent
Depending on the fibers being used and cement setting rates
desired, it may be desired to add a set accelerating agent to the
mixture. One well known suitable accelerating agent is calcium
chloride. It increases the speed of the initial set of the portland
cement but does not materially affect the final strength thereof.
Thus in a few hours, concrete containing a small amount of calcium
chloride will show higher compressive strength than concrete
containing no calcium chloride, but the two samples will have the
same strength after twenty-eight days of curing. Other salts such
as sodium sulfate or sodium chloride may also be employed.
A number of important advantages are obtained through the addition
of a suitable accelerating agent. Such a substance will speed the
curing of cement at the interface between the wood fibers and the
cement so as to partially offset the retarding effects of the
inhibitors in the wood fibers. However, depending on the fiber
compositions being used, the mere addition of calcium chloride to
the aqueous wood fibers/portland cement mixture, without
pre-treatment with dichromate, can result in composite materials of
markedly less strength than if dichromate is used.
It is important that the calcium chloride, if used, be added
immediately prior to the addition of the cement. This promotes the
concentration of the accelerator at the interface between the fiber
and the cement.
Triethanolamine (hereinafter referred to as TEA) has been reported
to be useful as an accelerator for the cure of portland cement when
used in small quantities. We found it to be effective for our
system but care must be taken to keep the amount small and to add
it after the addition of the cement. The substance acts at least to
some extent as a surfactant and if added before the cement, it
apparently causes the release of additional and harmful quantities
of the compounds which retard the set of portland cement.
The advantage of using TEA rather than calcium chloride as an
accelerator is that TEA is far less corrosive than the calcium
chloride and therefore much more useful when metals--such as nails,
reinforcing rods, etc.--are to be in contact with the product.
Advantage may also be taken of the process by which the portland
cement sets. FIG. 2 depicts a graph showing the relationship
between compressive strength and curing time for a typical concrete
mixture. Point A on the curve of FIG. 2 is arbitrarily selected for
illustrative purposes as the point at which the concrete mixture
must be placed in the mold. Placement before this point would waste
mold time, and placement after this point would reduce final
strength of the product as crystal formations would have advanced
beyond the point where they could be disturbed without serious
damage. Point B in FIG. 2 is arbitrarily selected for illustrative
purposes as the point at which the curing of the concrete has
advanced sufficiently to ensure dimensional stability upon removal
of the product from the molds. Thus, the curing cycle of the
concrete is divided into three phases:
Phase I: The induction of pre-curing phase between mixing and point
A;
Phase II: The molding phase between point A and point B when the
product is in the mold;
Phase III: The curing phase after the product has been removed from
the mold.
In the actual manufacturing operation, it may be desirable to
permit the final mixture to pre-cure a predetermined time before
placing it in the molds. This will reduce the amount of time that
the mixture must remain under compression in molds. This is
important from an economic viewpoint because stack press machines
(hereafter described) which are effective to form products from the
present mixture are expensive. By minimizing the molding time a
given stack press can be utilized more efficiently to produce a
maximum amount of product.
It should be emphasized that points A and B on the curve of FIG. 2
are arbitrarily selected for illustrative purposes and must be
accurately determined by experimentation for a given
fibers/portland cement system depending upon its composition. When
higher concentrations of silicates, i.e., greater than four percent
of the cement, are used, the mixed products can be put in molds
immediately after mixing and placed in the press. The accelerated
curing rate permits the precure step to be bypassed. The method of
the present invention is keyed or coordinated with the curing cycle
of the particular concrete mixture (the fibers/portland cement
mixture) in order to reduce molding time and thereby achieve a
continuous production of a large quantity of product with a minimum
amount of capital investment for equipment.
The Molding Parameters
A composite product with superior strength and surface texture can
be formed from a fibers/portland cement mixture by molding the same
under compression at an elevated temperature. A molding pressure of
between approximately 150 psi and approximately 600 psi at a
molding temperature of between approximately 120.degree. F. and
approximately 220.degree. F. will produce useful products. If
soluble silicate is present in amounts less than equivalent to
about eight percent 41.degree. Be' waterglass, a molding time of
one hour or more will be required. However, if the silicate is
increased to the equivalent of twelve to sixteen percent
waterglass, the molding time can be reduced to as short as fifteen
minutes for a five-eights inch thick product. Satisfactory products
can be obtained by molding at ambient temperatures, but the molding
time must be extended substantially. The optimum molding pressure
and temperature must be determined experimentally and will depend
upon primarily the composition of the fibers, the type of portland
cement used, and the presence of an accelerator. A molding pressure
of approximately 400 psi to approximately 500 psi and a molding
temperature of approximately 150.degree.-170.degree. F. have been
found to produce good results for the wood fibers/cement mixtures
experimentally tested by us. It is preferable that such a mixture
be maintained at a temperature of approximately
150.degree.-190.degree. F. throughout the molding operation. In
order to accomplish this, a live steam atmosphere may be utilized
as later explained. A humidified atmosphere during molding is
helpful depending on the design of the molds since it prevents
undue loss of moisture which might otherwise occur at the elevated
molding temperatures. Excessive moisture loss weakens the finished
product.
EXAMPLES
A number of experiments were performed in order to confirm the
advantageous effects of soluble silicates and dichromate ion or
permanganate ion in a wood fibers/portland cement composite.
Standardized procedures were used so that comparisons between many
different samples were prepared from a variety of woods and cement
would be meaningful. Mixing was done by hand to the extent that a
reasonably homogeneous mix was obtained. Usually a mixing time of
not less than two minutes was required. All samples were molded in
wooden or steel molds having internal dimensions of 6" by 4" by
5/8". The time that the mixture was allowed to stand in the molds
was varied depending upon the type of cement, temperature,
accelerator concentration and the like. With REGULATED SET cement,
the molding time was approximately 30 minutes at a temperature of
approximately 180.degree. to 212.degree. F. With type III portland
cement, the molding time was one hour unless stated otherwise.
After the samples were removed from the molds, some were tested
immediately and some were allowed to stand for 14 days from the
time of initial mixing before being tested for modulus of rupture
(MOR). During this 14 day period, the samples were kept at
60.degree. to 80.degree. F. The samples were kept in a humid
atmosphere after molding for a few days to prevent water loss. MOR
measurements were made using a Dillon tester. The samples measured
approximately 4 inches wide by 5/8 inch thick and the span used for
the test was 4 inches.
EXAMPLE I
The desirable effects of pre-treating western red cedar fibers with
dichromate ion are shown in Table I. A sample of crushed shavings
of western red cedar, generally about 3/4" by 1/4" by 0.02-04",
together with water, alum and sodium dichromate, was heated for
half an hour in boiling water in a closed glass container. A
duplicate sample of western red cedar without dichromate was
similarly heated. Calcium chloride was added to both samples to
accelerate setting of the portland cement. The dichromate solution
used was 10% weight/weight and the calcium chloride solution was
33% weight/weight. After the heat treatment, the material was
treated with waterglass and cooled and the Type III portland cement
was added in the amount indicated. After thoroughly mixing the
cement with the treated fibers, the mixture was placed in molds and
pressed to produce test specimens approximately 4" by 6" by 5/8"
thick. The final pressure was between about 270 psi and 300psi.
After a period of one hour, the molds were opened and the samples
allowed to stand open to air at ambient conditions for 14 days for
further curing of the cement. They were tested for their moduli of
rupture using a Dillon tester as described above. The sample made
with sodium dichromate had far superior strength.
EXAMPLE II
Although douglas fir is far less difficult than cedar to bond with
Type III portland cement, such a composite can be improved
substantially in strength with the dichromate treatment especially
if the fir is freshly cut. Such treatment is very important for
fast, high temperature molding. Fir planer shavings less than a
month old hammermilled with a 3/16" screen were used to make test
samples with results shown in Table II. In all cases the samples
were pressed for one hour at about 400 psi at
200.degree.-212.degree. F., and then tested two weeks later.
EXAMPLE III
Similar improvements can be obtained with the fast setting
REGULATED SET cement. The strength of these composites, however,
were not quite as high in the case of cedar fiber as with Type III
cement, but were very good in the case of hammermilled douglas fir
fibers. These results are shown in Table III. Hammermilled planer
shavings of wood, either cedar tow or douglas fir; about 1" or less
in length and about 1/8" or less in width were used. The shavings
were added to 10% w/w potassium dichromate solution, along with
water, 20 grams of slaked lime, and 120 grams of REGULATED SET
cement. The mixed portions were compressed in steel molds at
approximately 500 psi. The compressed composites were then removed
from the molds and allowed to cure in ambient conditions for 14
days prior to testing.
Since REGULATED SET has a very rapid rate of set, it is necessary
to add a controlling chemical. Slaked lime appears to be slightly
better than plaster paris for this purpose in these samples.
Samples 8-10-4 and 8-10-5 were cured for 30 minutes in a steel mold
in steam at atmospheric pressure. The others were cured at room
temperature overnight.
EXAMPLE IV
In Table IV, the effect of varying the ratio of cedar tow
(hammermilled with 1/4" screen) to Type III portland cement is
shown. The cedar fibers, which had a moisture content of 10.8%,
were first treated with 4% of their weight of sodium dichromate
dihydrate in water. Calcium chloride in proportion of 5% of the
cement presented was also added. Sample 10-8-1 was held under 300
psi for 12 hours, the other pressed at 600 psi for the same period.
All were cured for 14 days prior to strength testing. As shown in
the table, effective strengths can be obtained over a relatively
wide range of cement/fiber ratios but they appear to peak around
1.6:1 in these cases.
EXAMPLE V
A further example of the method of the present invention is set out
hereafter:
______________________________________ Sample Composition (Sample
2-159-4) Cedar tow, hammermilled with 1/4" 141 g. screen moisture
content 30.5% Alum solution (20% w/w) 18 ml. Sodium dichromate
dihydrate 39 ml. solution (10% w/w) Waterglass solution (1 part 39
ml. 40.degree. Be/2 parts water) Calcium chloride solution (33%
w/w) 6.5 ml. Type III portland cement 108 g. Procedure 1. The
dichromate and alum solutions were mixed, then added to the cedar
fiber, mixed thoroughly therewith and let stand for 30 minutes at
100.degree. F. 2. Next the waterglass solution was added. 3. Next
the calcium chloride solution was added. 4. Finally the portland
cement was added. 5. The mixture was pressed in steel molds of in-
ternal dimensions of 6" by 4" by 5/8" (pressure to close the mold
was 460 psi). 6. The mold was maintained in a closed container over
boiling water vented to atmospheric pressure for 60 minutes. 7. The
sample was then removed from the mold and allowed to cure at
ambient room conditions for 14 days.
______________________________________
The final product had a density of 68 pounds per cubic foot and MOR
of 1448 psi.
EXAMPLE VI
In Table V the effects of adding sulfite to various samples of
hammermilled fir planer shavings are shown. In one case (7-199-1)
sodium sulfate, which is the oxidation product of sodium sulfite,
was added to see if this compound was the cause of the significant
increase in strength resulting from sulfite addition. The tests
showed the product with sodium sulfate had less strength than the
same product using sodium sulfite, but either additive caused an
increase in strength over the control, Sample No. 8-229-4, see
Table V.
EXAMPLE VII
The effect of quantity of the triethanolamine (TEA) on the strength
of the composite is shown in Table VI. The need for carefully
maintaining a low concentration of the TEA is evident.
EXAMPLE VIII
Still another example of the present invention is set out
hereafter.
______________________________________ Sample Composition (Sample
8-289-1) Fir hammermilled planer shavings, 90 g. (OD) 1/4" screen,
moisture content = 26.4% Sodium thiosulfate trihydrate 5 g. Alum
solution 20% w/w aluminum sulfate 20 ml. Water 10 ml. Sodium
dichromate dihydrate solution 15 ml. Waterglass solution, 2:1
water:41.degree. Be' 30 ml. sodium silicate Type III portland
cement 135 g. Triethanolamine solution 1% w/w 14 ml. Procedure 1.
The alum and sodium thiosulfate solution were mixed and immediately
thereafter mixed with the fir. 2. Allowed to stand 5 minutes at
room temperature with frequent stirring. 3. The dichromate solution
added and the mixture heated 15 minutes in steam bath. 4.
Thereafter cooled waterglass mixed in, then the Type III cement. 5.
The solution of triethanolamine quickly added and mixed. 6. Pressed
into a steel mold having a cavity of approximately 4" by 6" by
5/8", using a pressure of 500 psi to bring the thickness just to
5/8". 7. Placed in a humid atmosphere at a temperature of 150 to
170.degree. F. and held there under pressure for one hour. 8. The
sample was removed from the mold and lightly sprayed with about 3
ml. of water to assure a moist condition, then stored in a water
vapor tight container for 2 days at 90-100.degree. F. 9. Thereafter
it was removed from the container and allowed to stand under
ambient room condi- tions for 14 days to complete the cement cure.
______________________________________
The final product had a density of 72 pounds per cubic foot and a
MOR of 1536 psi.
EXAMPLE IX
The beneficial effect of potassium permanganate treatment was shown
in other tests set forth in Table VII. In these tests oven dried
cedar shavings hammermilled with a 3/16" screen were used in the
tests, all weights are in grams.
EXAMPLE X
A series of tests were carried out to test the relative effect of
using higher concentrations of waterglass with Douglas fir fiber
treated with sodium dichromate where the initial press was carried
out at high temperatures. The results are shown in Table VIII. In
these samples the fiber was prepared by hammermilling with an 1/8
inch screen Douglas fir planer shavings. The waterglass where added
was added after treatment of the fibers with sodium dichromate and
before the addition of cement. In all instances 3 parts of cement
were used for each part of fiber. Sodium dichromate and waterglass
(as 41.degree. Be') and hydrochloric acid are expressed as parts by
weight. The samples were pressed at 500 p.s.i. and held in a steam
atmosphere for twenty-four minutes. They were tested fifteen
minutes after removal from the mold.
EXAMPLE XI
The effect of the order of addition of cement and waterglass was
tested. As shown in Table IX no significant difference in result
occurs. In one procedure (Tests 12-10-1) hydrochloric acid and
waterglass were mixed. The resulting gel was mixed with Douglas fir
derived fiber. Finally Portland cement was mixed in.
In other samples (Tests 11-60-6 and 11-60-6A) Douglas fir fiber was
wetted with water, Portland Cement then mixed with the fiber, and
finally a mix of waterglass and hydrochloric acid added.
In still other samples (Tests 11-60-5 and 11-60-5A) Douglas fir
fiber was wetted with hydrochloric acid. Waterglass was then mixed
with the fiber and finally Portland cement added.
In all instances 3 parts of Type III Portland cement, 0.36 parts of
41.degree. Be' waterglass, 0.36 parts 2.5 N hydrochloric acid, and
approximately 1.32 parts water were used for each part of
fiber.
After mixing the samples were placed under an initial 500 p.s.i.
pressure and heated in steam for 24 minutes. Samples retained for a
two week test were placed in plastic bags and held at room
temperature.
EXAMPLE XII
Another series of tests were conducted with Douglas fir fiber to
determine the effect of different amounts of waterglass. The fiber
was prepared by hammermilling planer shavings using an 1/8 inch
screen. Parts will be given by weight. One part of fiber (oven dry
basis) previously washed with boiling water was mixed with 2.5 N
hydrochloric acid and then a dilute solution of 41.degree. Be'
waterglass. Thereafter 3 parts of Type III cement was mixed in,
samples were placed in molds and pressed to an initial 500 p.s.i.
and placed for twenty minutes in an atmosphere of live steam.
Fifteen minutes after removal from the steam some samples were
tested. Others were placed in plastic bags and tested after two
weeks at room temperature. These tests, as shown in Table X,
demonstrated increasing amounts of sodium silicate gave increasing
out-of-the-mold strength, but that the two week strength peaked at
about sixteen percent waterglass.
EXAMPLE XIII
Tests were carried out to determine if calcium chloride, a known
set accelerator, could give the same beneficial effects as does the
addition of waterglass. In one sample (10-30-2), one part of water
washed fir was mixed with three parts of Type III cement, 0.06
parts calcium chloride, and one and one-half parts of water. In
another sample (10-30-3), the calcium chloride was omitted and 0.36
parts of hydrochloric acid, then 0.36 parts of sodium silicate were
substituted. Both samples were pressed to an initial pressure of
500 p.s.i. and subjected to an atmosphere of steam for twenty
minutes, and then removed from the mold. When tested one hour
later, sample 10-30-2 with the calcium chloride had an MOR of 21.
Sample 10-30-2 had an MOR of 334.
EXAMPLE XIV
As shown in Table XI, sodium silicate when used in combination with
sodium dichromate treatment of western red cedar fibers, enhances
the out-of-mold strength substantially. In these tests, western red
cedar hammermilled planer shavings, 1/8 inch screen, were treated
with sodium dichromate. Acidified sodium dichromate solutions (by
addition varying amounts of sodium dichromate to 2.5 N hydrochloric
acid) were added to the cedar. Then, after reaction was essentially
complete, an aqueous solution of 41.degree. Be' waterglass was
added. Finally, Type III cement was added. The samples were pressed
at 500 p.s.i. initial pressure and held for 24 minutes in
atmospheric steam. solution of 41.degree. Be' waterglass was added.
Finally, Type III cement was added. The samples were pressed at 500
p.s.i. initial pressure and held for 24 minutes in atmospheric
steam.
In summary, in accordance with our rapid set process the
cement/fiber/high ratio silicate mixture is set under high
temperature (preferably 175.degree.-180.degree. F.) and high
pressure. This temperature should be reached within twenty minutes
or less. This enables the product to gain sufficient strength to be
removed from the mold and processed. Moreover, the product will
continue a rapid rate of cure and will attain within twenty four
hours eighty percent of its ultimate strength. High strength of
product can only be obtained, however, when substantial amounts of
silicate are utilized. For example, twelve percent waterglass is
necessary with Type III portland cement to obtain maximum fourteen
day strength with untreated Douglas fir fiber.
The Manufacturing Process
The following discussion taken in conjunction with FIG. 1 will
provide an understanding of the overall operation of a suitable
manufacturing process of the present invention. This example
describes the procedure for making roofing shingles approximately
sixteen inches long, of various widths, and having a shape and
thickness similar to shingles typically sawn from cedar wood.
Modifications in the various equipment and other details described
which may be necessary to produce other composite building
materials such as siding will occur to persons skilled in the
art.
The wood fibers (douglas fir, western red cedar, or pine, etc.) are
mechanically prepared in a conventional manner. Plane shavings or
flaked shavings may be utilized. These shavings can be reduced in
size by running them through a hammermill or through a disk
refiner. For shingles, wood particles produced by hammermilling and
passing a 1/8" screen are preferably used. However, a wide
variation in particle sizes may be used according to the present
invention depending upon the desired characteristics of the end
product.
After a pre-curing period, if such is utilized, the mixture is
agitated in a suitable mixer and delivered to a dispensing hopper
10 (FIG. 1). Wood fiber/portland cement mixture delivered from the
dispensing hopper is formed into a product mat 12 of proper size
and weight on a horizontal conveyor 14. Generally the mat is wide
enough to form several shingles thereacross. The mat is relatively
thick, and uncompressed at this point. The conveyor 14 transports
the uncompressed mat 12 onto a second conveyor 16 which carries the
mat under a compression roll 18. The blanket is compressed to a
predetermined thickness by the roll 18 to provide mat integrity for
subsequent operations. For example the compression at this point
may reduce the mat 12 to approximately fifty percent of its
original thickness.
The conveyor 16 then moves the compressed mat 12 under a
reciprocating knife 20 which cuts the mat into discrete portions
12' which are long enough so that the finished shingles will be
approximately 16 inches in length when completely cured. The
portions 12' of the mat are carried by the second conveyor 16 to a
caul plate applicator 22 where a bottom caul plate 24 is placed
underneath each portion 12' of the mat, and a top caul plate 26 is
placed on top of each portion. The caul plates 24 and 26 may be of
aluminum or other metal, such as iron or steel, and are large
enough to enclose the portion 12'. The caul plates are embossed to
give the product its desired shape and prevent the mat portions 12'
from sticking to the platens of the later described stack press. In
addition, the caul plates serve as carriers by which the portions
of the mat are carried through the multiple stations of the
equipment to be formed into shingles.
Preferably a suitable caul plate release agent, such as zinc
stearate or Teflon coating, is used to prevent the mat portions 12'
from sticking to the caul plates. The caul plates present a smooth
base to the mat portions 12' and this insures a flat, smooth
surface on the cured shingles. The caul plates are configured to
form several shingles across a mat portion which is later sawed
apart.
The now sandwiched mat portions 12' are deposited upon a
conventional stack press loader 28. It may comprise a platform
portion 30 upon which each of the sandwiched mat portions 12' is
sequentially positioned. A hydraulically operated plunger 32 raises
or lowers the sandwiched mat portions to the bottom of a multiple
opening vertical stack press 34. The construction of the stack
press will not be described since it does not comprise part of the
present invention. Typical stack press designs are disclosed in
U.S. Pat. Nos. 3,126,578; 3,478,137; 3,542,629; and 4,148,857.
The pairs of caul plates 24 and 26, each loaded with a mat portion
12' sandwiched therebetween are conveyed sequentially into the
entrance position at the bottom of the stack press. The stack press
34 in general comprises a series of vertically spaced pairs of
heated platens. The loaded pairs of caul plates are received in the
openings defined between the pairs of platens. After each of the
openings has received a loaded pair of caul plates, the press is
then operated so as to apply heat and pressure uniformly to the
just inserted mat portion 12'. Preferably the press is heated
internally so that the heat from the platens will insure that the
mat portions will be heated to and maintained at a temperature of
approximately 200.degree. F. while they are in position throughout
the stack press. The product is preferably enveloped in an
atmosphere of live steam at a temperature of approximately
200.degree. F. while in the press.
As each mat portion 12' sandwiched between upper and lower caul
plates 26 and 24 is received in the entrance opening at the bottom
of the stack press 34 it is pressed to suitable stops, preferably
at a pressure of about 150 to 500 psi. Preferably the volume of the
mat portions is reduced during the initial compression to below
that required for the final product. Thereafter the portions are
allowed to expand slightly to establish their final product volume.
This permits the final product volume to be maintained with
considerably less pressure than required to effect the initial
product volume in the first place. The pressure required after the
initial compression can be supplied by the weight of the loaded
caul plates stacked above a given mat portion. The portions are
maintained under pressure for a predetermined time interval which
is sufficient to insure that their dimensional integrity will be
preserved upon release from the stack press. Again, this time
interval is determined experimentally depending upon the
composition of the wood fiber/portland cement/dichromate/waterglass
mixture. As previously indicated, however, by coordinating the
steps of the mechanical process precisely with the curing curve,
the total molding time can be reduced to two hours or less.
The stack press 34 is preferably one constructed so that the loaded
caul plates are released at the top of the stack press and are
removed one at a time as a unit without releasing pressure on the
entire stack. When removed from the top of the stack press the
loaded caul plates are received by a conventional stack press
unloader 36 which may have a construction similar to the stack
press loader 28. The loaded caul plates are lowered by the unloader
36 to the work floor level where the compressed shingles are
removed from the caul plates by suitable means such as a vacuum
lift.
The shingles are then passed through suitable saws to trim their
edges. Normally since the mat portions 12' are each compressed into
a plurality of shingles the now compressed mat portions must be cut
into individual pieces. The individual shingles may now undergo
further fabrication which may include waterproofing through use of
stearates and other similar materials. The caul plates pass by
another conveyor (not shown) through a cleaning station and to a
station where caul plate release agent is again applied. Thereafter
the caul plates are recycled to form additional shingles. The
shingles may be secured together in bundles so that after
sufficient curing at ambient conditions (60.degree. to 80.degree.
F.), they may be shipped.
A modification of the above arrangement is preferably utilized. In
this arrangement a series of molds may be carried beneath a
dispensing hopper and filled with the material to be pressed
similarly to the procedure described above. After compression and
trimming of the excess material from the molds, they can be passed
over a scale to ascertain that each is loaded with a sufficient
amount of material. Thereafter, the plurality of the molds are
stacked in a group of a desired number which may be, for example,
twenty-four molds. These are pressed together in a conventional
hydraulic press and stress rods applied to maintain the stack in
its compressed condition. This stack is then passed through a
heating tunnel in which a steam atmosphere is maintained so as to
heat the molds and, more particularly, the portland cement-fiber
mixture to the desired setting temperature. After a proper time
within the oven, the stacks are discharged and disassembled and the
molded products removed from the molds which can then be recycled
for further processing. The molded products are trimmed and
subjected to such further fabrication as may be desired.
Having described preferred embodiments of the composition of
matter, improved building materials, and method of producing the
same, it will be apparent to those skilled in the art that the
invention permits of modification in both arrangement and detail.
However, the present invention should be limited only in accordance
with the scope of the following claims.
TABLE I
__________________________________________________________________________
Sodium Water- Calcium Water Cement Product Wood Dichro- glass
Chlor- (all Type Den- OD MC Alum mate g. ide sources) III sity MOR
Sample g. % g. g. 41.degree. Be' g. g. g. lb/ft.sup.3 psi
__________________________________________________________________________
2-169-1 97 9.6 3.6 None 12.7 5.5 107 109 55 497 2-169-2 97 9.6 3.6
4.3 12.7 5.5 107 109 62 1157
__________________________________________________________________________
TABLE II
__________________________________________________________________________
Beneficial Temperatures Hammer- Sodium Water- Calcium Water Cement
Product Fir mill Dichro- glass Chlor- all Type Den- OD Screen MC
Alum mate g. ide sources III sity MOR Sample g. Size % g. g.
41.degree. Be' g. g. g. lb/ft.sup.3 psi
__________________________________________________________________________
3-189-1 95 3/16" 23.2 2.8 None 9.8 3.8 103 104 58 268 3-189-2 95
3/16" 23.2 2.8 3.4 9.8 3.8 101 104 63 1106 4-279-2 70 3/16" 18.6
2.9 2.4 10 5.0 80 162 74 1080 4-279-3 70 3/16" 18.6 2.9 None 10 5.0
82 162 62 386
__________________________________________________________________________
TABLE III
__________________________________________________________________________
Cedar Tow Fir 10% (grams (grams Potassium Water REGULATED oven dry
oven dry Dichromate (grams, all SET MOR Sample basis) basis)
(grams) sources) (grams) (PSI)
__________________________________________________________________________
7-11-2 -- 75 3.6 100 120.sub.(a) 1328 7-11-4 -- 75 -- 100
120.sub.(a) 786 7-29-3 54 -- -- 90 120.sub.(b) 157 7-29-4 54 -- 3.6
100 120.sub.(b) 744 8-22-1 -- 75 3.6 100 120.sub.(b) 1418 8-10-4 --
73 -- 100 120.sub.(c) 800 8-10-5 -- 73 3.0 100 120.sub.(c) 1018
__________________________________________________________________________
.sub.(a) 20 g. lime added to control set .sub.(b) 5.4 g. plaster
paris added to control set .sub.(c) mixture of 10 g. lime and 10 g.
plaster paris added to control set
TABLE IV
__________________________________________________________________________
Cedar Cement Tow Sodium Calcium Water Type Ratio Density (grams)
Dichromate Chloride (grams, all III Cement/ (lb./ MOR Sample (a)
(grams) (grams) sources) (grams) OD Cedar cu. ft.) (PSI)
__________________________________________________________________________
10-8-1 62 2.3 6.0 100 120 1.9 63 942 10-8-2 68 2.6 5.7 99 114 1.7
62 1240 10-8-3 73 2.7 5.4 98 109 1.5 60 1209 10-8-4 78 2.9 5.2 94
104 1.3 55 1021
__________________________________________________________________________
TABLE V
__________________________________________________________________________
EFFECT OF SULFITE TREATMENT OF FIBERS ON STRENGTH OF PRODUCT 20%
Sodium 20% Sodium Sodium 2:1 40.degree. Be' Type III Mold Sample
Fiber Sulfite Alum Dichromate Water Sulfate Waterglass Cement
Pressure No. (grams) (grams) (ml.) (ml.) (ml.) (grams) (ml.)
(grams) (psi) MOR
__________________________________________________________________________
8-229-4 80.sub.(b) -- 20 20 14 -- 40 135 500 1209 8-229-5
80.sub.(b) 4.7 20 20 14 -- 40 135 500 1520 7-199-1 100.sub.(a) --
20 15 30 7.5 40 130 500 1399 7-199-2 100.sub.(a) 4.0 20 15 30 -- 40
130 500 1589 8-39-4 100.sub.(c) 4.0 20 15 45 -- 40 130 500 1802
__________________________________________________________________________
.sub.(b) Fir hammermilled planer shavings 3/8" screen, moisture =
26.4% .sub.(a) Fir hammermilled planer shavings 1/8" screen,
moisture = 10.4% .sub.(c) Fir hammermilled planer shavings 3/8"
screen, moisture = 11.6%
TABLE VI ______________________________________ Sample
Triethanolamine (a) (% of cement present) MOR
______________________________________ 8-309-1 0.10 1582 8-309-2
0.25 1287 8-309-3 0.40 1087 8-309-4 -- 1271
______________________________________ (a) All samples consisted of
90 g. fir hammermilled planer shavings 1/4" screen, mixture content
= 26.4%, 20 ml. of 20% w/w alum, 15 ml. of 20% w/ sodium
dichromate, 10 ml. water, 20 ml. of 2:1 diln. of 41.degree. Be',
waterglass, and 135 g. Type III cement. Measured amounts of
triethanolamine were added in a total of 14 ml. of water in each
case.
TABLE VII
__________________________________________________________________________
Cement Water- Calcium Type Closing Sample Cedar Alum KM.sub.n
O.sub.4 glass Chloride Water III Pressure Density No. g. g. g. g.
g. g. g. (psi) lb/ft.sup.2 MOR
__________________________________________________________________________
4-149-1 85 6.2 3 20 3 96 114 330 61 599 4-149-2 85 6.2 -- 20 3 96
114 350 58 292
__________________________________________________________________________
TABLE VIII
__________________________________________________________________________
Water Fiber Sodium 41.degree. Be' All Sources Cement MOR (OD) 2.5 N
HCl Dichromate Waterglass Except Waterglass Type III 15 min. Sample
No. g. ml. g. g. ml. g. Out of Mold
__________________________________________________________________________
11-250-2 50 18 0 18 67 150 128 11-250-2A 50 18 0 18 67 150 125
11-250-5 50 18 0 18 67 150 140 11-250-3 50 18 1.6 18 67 150 158
11-250-3A 50 18 1.6 18 67 150 145 11-250-4 50 18 1.6 18 67 150 161
__________________________________________________________________________
TABLE IX ______________________________________ Effect of Order of
Addition of Silicate MOR Sample After 15 min. After 2 weeks
______________________________________ 11-60-5 156 11-60-5A 1563
12-10-1 172 11-60-6 178 11-60-6A 1404
______________________________________
TABLE X ______________________________________ 41.degree. Be'
Sodium Average sample MOR Silicate-% thickness-in. 15 by wt. of Out
At Min. After portland of break out of 14 Sample cement mold time
Change mold days ______________________________________ 10-150-5 0
0.586 0.611 +0.025 20 532 10-150-6 4 0.563 0.576 +0.013 23 878
10-150-7 8 0.554 0.558 +0.004 62 1262 10-150-8 16 0.557 0.562
+0.005 213 1490 10-150-9 24 0.582 0.582 0 284 1407
______________________________________ Parts by weight Ingredient
______________________________________ 0.33 Fir, hammermilled
planer shavings, 1/8 in screen; washed with boiling water; OD basis
0-0.18 2.5 N Hydrochloric acid 0-0.18 41.degree. Be' waterglass 1.0
Portland cement 0.5 Water from all sources
______________________________________
TABLE XI
__________________________________________________________________________
Effect of sodium silicate concentration on the initial strength of
composites containing western red cedar
__________________________________________________________________________
Sodium Sil- Sodium Di- icate as chromate 41.degree. Be' Water-
Thickness MOR % of OD glass % of Out of After After Sample Cedar
Cement Mold 15 min. Change 15 min.
__________________________________________________________________________
11-200-1 3 0 0.644 0.668 +0.024 20 11-200-2 3 7.4 0.621 0.624
+0.003 174 11-200-3 3 16 0.652 0.655 +0.003 293 11-200-4 3 23 0.662
0.664 +0.002 241 11-200-5 0 7.4 0.625 0.636 +0.011 30
__________________________________________________________________________
Initial Set Condition: 24 min. in atmospheric stem, mold pressure
500 p.s.i. Sample Compositions: Parts by weight Ingredient
__________________________________________________________________________
1 Western red cedar hammermilled planer shavings, 1/8" screen
0.22-0.66 2.5 N. Hydrochloric acid 0.03 Sodium dichromate 0.22-0.70
411/4 Be' waterglass 1.7 Water all sources 3 Type III cement
__________________________________________________________________________
* * * * *